Power converters are commonly used to convert AC power from a generator to DC power, and then from DC power to AC power for use by a motor. Power conversion requires high-speed switching of large currents by power semiconductor devices, such as insulated gate bipolar transistors (IGBTs). Bulk capacitance is needed to dampen ripple current that occurs on the DC link that connects the different power conversion stages. The bulk capacitance also serves to filter out harmonic content and voltage spikes of the DC link voltage. Film capacitors are often the preferred choice for mobile applications and can be packaged and mounted in a variety of ways.
High vibration (up to 30 G) environments associated with heavy duty mobile applications increase the loads seen by electronic components. The large mass of the film capacitor package further increases the loads caused by vibration. The increased loads can lead to failures of the capacitor if the design of the mounting arrangement does not properly account for them.
One example of a prior art mounting arrangement can be found in United States Patent No. 20110,181,105 to Michinaka et al., issued Jul. 28, 2011, entitled “POWER CONVERSION APPARATUS FOR VEHICLE USE.” FIG. 14 of Michinaka shows that there is a large distance between the mounting surface adjacent to mounting legs 37 and the center of mass of the capacitor module 17 (center of mass can be estimated from the figure). This large distance results in a large moment created by vibration forces. Further, the mounting legs 37 have a small thickness and therefore offer insufficient bolt stretch to maintain a proper bolted joint when subjected to high vibration forces. Therefore, it is seen that the design of Michinaka is not suited for heavy duty applications that are subjected to high vibration.